Converting from an auto to a manual (or vice versa) very rarely goes smoothly and often causes all kinds of unforeseen headaches (and bills). It's also expensive and unlikely to add any value to the car. If your car is unmodified and original, it will be worth more if you keep it that way. If you are serious about doing this, try and find some owners that have done it and take onboard their experiences. And make sure you drive their cars - the manual box isn't always to everyone's tastes. You don't mention why you want to do this. If it's to improve fuel economy, you'd need to cover a huge amount of miles to make the cost of the conversion worthwhile (if it all), and if you're looking for more performance, there might be simpler ways to achieve this.